1. Field of the Invention
The present invention relates to a zoom lens system having an image-stabilizing function.
2. Description of Related Art
An image sensor used in a compact digital camera typically has a size of about 1/2.5-inch through 1/1.7-inch, in which high pixelization is achieved by miniaturizing the pixel pitch. However, in recent years, the pixel pitch has been reduced down to approximately 1 through 2 μm, and further improvement of the image quality cannot be expected. The use of a large image sensor which can enlarge the pixel even in a compact digital camera is known to achieve a higher quality, in the real sense. However, if the image sensor is enlarged, the optical system also increases in size to the extent that such an optical system cannot be accommodated in a compact digital camera. In particular, in a zoom lens system equipped with a so-called optical image-stabilizer (shake-correction device), in which part of the zoom lens system is driven in directions orthogonal to the optical axis in accordance with the magnitude of hand shake, etc., that is applied to the camera in order to correct image shake, when an entire lens group of one of the movable lens groups thereof, which are moved during zooming, is driven in order to correct image-shake (which is often carried out in a compact digital camera), the mechanical burden on this movable lens group is large and it is difficult to miniaturize the lens unit thereof.
Out of negative-lead zoom lens systems, in which the frontmost lens diameter thereof can be reduced, zoom lens systems having a negative lens group, a positive lens group and a positive lens group, in that order from the object side, (i.e., three lens groups) having favorable telecentricity and few backfocus restrictions are often used in compact digital cameras that do not have an interchangeable lens barrel. In such a type of zoom lens system, it is very common for the third lens group which is provided close to the camera body (and is easily driven) to perform a focusing operation to serve as a focusing lens group, and for the entire second lens group that has a relatively (compared to the first lens group and the third lens group) small diameter to serve as a image-stabilizer lens group (shake-correction lens group). However, if the size of the image sensor is increased, since the entire zoom lens system is enlarged accordingly, although the outer diameter of the zoom lens system may be small, if the entire second lens group is utilized to serve as a image-stabilizer lens group, the mechanical burden is increased.
Furthermore, Japanese Unexamined Patent Publication No. 2008-203344 discloses a zoom lens system having a negative lens group and a positive lens group, in that order from the object side (i.e., two lens groups), in which the entire second lens group serves as an image-stabilizer lens group. However, since this second lens group serving as an image-stabilizer lens group is configured of three lens elements, there is an increased burden on the driving device therefor.